1. Field of the Invention
The invention pertains to the field of lateral flow immunoassays. More particularly, the invention pertains to in situ lysis of samples in lateral flow immuonassays.
2. Description of Related Art
Lateral flow immunoassays combine the reagents and the process steps of more general immunoassays into an improved assay. This enables single-step, point-of care testing (POCT) and provides a sensitive and rapid means for detection of target molecules. Lateral flow immunoassays are available for a wide array of target analytes and can be designed for sandwich or competitive test formats. Generally high molecular weight analytes with several epitopes are analyzed in a sandwich format whereas small molecules representing only one epitope are detected by means of a competitive assay. The first lateral flow assays tested for human chorionic gonadotropin (hCG). Today commercially available tests monitor ovulation, detect infectious disease organisms, analyze drugs of abuse and measure other analytes important to human physiology. Products have also been introduced for veterinary testing, environmental testing, and product monitoring.
U.S. Pat. No. 5,714,341 discloses a lateral flow immunoassay for HIV specific antibodies in saliva samples. A saliva sample is diluted in a sample buffer, and a lateral flow immunoassay is dipped into the diluted saliva sample, again enabling point-of-care testing with rapid results.
German Patent DE19622503 discloses a lateral flow immunoassay for illegal narcotics in saliva and sweat.
There is a need for still simpler-to-use and more rapid lateral flow immunoassays suitable for time-sensitive and cost-sensitive clinical settings. This need is most acute in situations where the sample type and target analyte necessitate a sample preparation step. This may occur when an analyte is not readily presented within a sample and a separate lysis step is necessary to free the analyte for efficient presentation. Such an assay may need to directly test for analytes in human body fluids, including analytes which may be protected within complexes or behind cellular membranes.
As an example, fever is a common cause of childhood visits to urgent care centers for both family practice and pediatric offices. Most commonly, this relates to either a respiratory infection or gastroenteritis. The high incidence of fever in children and the precautions administration of unnecessary antibiotics is reason to develop a rapid screening test for biomarkers that distinguish viral from bacterial infections.
The efficiency and even the probability of success of a given immunoassay will depend on the initial presentation of any antigens to be detected. Antigens and other targets must be accessible to antibodies of an assay. Access can be impacted if most or all of the available antigen is masked in a complex or is inaccessible behind a cell membrane, e.g. in a cell's cytoplasm. In these situations, a viable and efficient assay may need to include a lysis step designed to make an antigen accessible, either by breaking up a complex to unmask components or by removing barriers such as a cell wall, a membrane of a cell or organelle, or a coat of a virus. However, such an added lysis step may complicate and delay an assay, even causing it to be too complex or time consuming for practical operation in a clinical setting.
In order to detect analytes protected within a complex of molecules or behind a membrane or other barrier, one approach in the immunoassay field is to lyse the complex or barrier and extract the analyte of interest prior to performing the immunoassay. When the barrier is a cell wall or cell membrane, the cells can be erythrocytes, leukocytes, epidermal, viral, fungal or bacterial, and they can be normal or malignant. Traditionally, a required lysis step is accomplished prior to and physically separate from the desired immunoassay, as a sample preparation step.
Practical operation in point-of care testing means that an assay needs to operate in such a manner as to report a result meeting point-of-care testing requirements including but not limited to timeliness, accuracy, sensitivity, specificity, and ease of use. Therefore, there is a need in the art for methods and devices that can circumvent the need for a separate lysis step prior to running a lateral flow immunoassay.